(a) Field of the Invention
This invention relates to liquid developers for use in electrostatic photography and to methods of manufacturing the same. The toner particles in the liquid developers are characterized by specific mean particle sizes of from 0.2 to 0.8.mu. , and a particle size distribution such that about 90% of the particles are in the particle size range of from 0.3 to 0.6.mu. .
(B) Description of the Prior Art
Wet-process electrophotography is preferred over the dry process because of advantages with respect to edge effects and reproducibility of the original image. Liquid developers for use in wet-process electrophotography are usually manufactured by blending pigments, high-molecular weight resins and a solvent, and subsequently dispersing the resulting blend in a petroleum hydrocarbon. A wide variety of resins and pigments have been employed. Utilizing conventional methods of manufacturing, the toners obtained usually have a mean particle size of from 0.4 to 0.7.mu. , but because of their wide range of particle size distribution, the resulting developers are so unstable that, when utilized for copying, the resulting images have poor contrast and stained backgrounds. Attempts to solve this problem by improving the solubility and hence the dispersibility of the resin have not been successful, because it is necessary to reduce the mean particle size of the toners to a range of about 0.1 to 0.3.mu. . As a result, it is very difficult to produce copies having high image density.